1. Technical Field of the Invention
The present invention relates to a method and apparatus for multiplexing coded voice data and fixed length message data requiring transmission within a maximum response time and, more particularly, a method and apparatus for controlling a rate of coding the coded voice data to transmit the fixed length message data within the maximum response time.
2. Description of the Related Art
Speech in known cellular telephones is detected by a microphone and coded by a vocoder. The vocoder provides coded voice data representative of the speech. Cellular telephones need to transmit control messages besides coded voice data. Known cellular telephone formats transmit the control messages in separate packets from the coded voice data. These separate packets of control messages and coded voice data are multiplexed to transmit them on a channel.
When a cellular telephone sends a control message to a base station, the base station typically must acknowledge receipt of the control message. In the round trip transmission of the control message from the cellular telephone or the acknowledgment from the base station, the transmitted radio waves may not reach their destinations. Atmospheric conditions, random reflections of the radio wave off buildings or hills, etc. can obstruct reception of the radio waves. When a radio wave is obstructed, a the cellular telephone should not have to wait indefinitely for the acknowledgment form the base station.
Control messages containing an acknowledgment have thus been required to be transmitted within a maximum response time. A cellular telephone waiting for an acknowledgment then knows that after the maximum response time, the acknowledgment must have either been sent and obstructed or the original control message never received due to atmospheric obstructions.
In a cellular telephone transmission system, several incompatible goals are pursued. The speech should be transmitted in real time without a reduction in quality. The speech must also be transmitted together with control messages using the smallest amount of data possible. Also, the transmission must conserve the limited radio spectrum and minimize interference with other users. Finally, as discussed above, a control message containing an acknowledgment must be promptly transmitted within a maximum response time. This invention provides for the transmission of message data within a maximum response time together with coded voice data and, in particular, sends the message data without a noticeable reduction in voice quality while conserving spectrum and reducing interference to other users.